This invention is directed to a steering mechanism primarily for lightweight, off-road vehicles such as snowmobiles, all terrain vehicles and lawn tractors.
Motorized off-road vehicles generally include a frame or chassis, two steerable skis or wheels at the front, a motor mounted in the front portion of the chassis, and an endless track or wheels attached to the rear portion of the chassis driven by the motor to propel the vehicle. Typical prior art steering mechanisms include handlebars or a steering wheel mounted atop a steering post with a transfer arm attached to the lower end of the post. The steering post is rotatably attached to the chassis at one or more points and typically extends underneath the motor. Movement of the steering post is transmitted to a steering arm by means of a transfer arm. The transfer arm typically takes the form of a threaded tube with a pivoting joint at each end, a rack and pinion assembly, or a steering box that encloses gears. The steering arm is usually attached to a drag link that is, in turn, pivotally attached to the chassis using an idler arm. The drag link then transfers motion to a pair of tie rod tubes fitted with a tie rod on each end. The tie rod tubes are attached to a pair of spindles, which support the wheels or skis and transfer the steering motion from the handlebars or steering wheel.
One obvious disadvantage of a conventional steering system is the large number of individual component parts and pivot points utilized, adding weight and expense to the steering system. Each of these parts is subject to wear, some parts wearing quite quickly, creating an undesirable amount of free play in the handlebars which can result in binding of the entire steering mechanism. Furthermore, many of these component parts are located beneath the motor which has two disadvantages. First, this configuration requires the motor to be mounted high on the chassis, producing a high center of gravity and a vehicle with poor ergonomics necessitating a high cowl which has poor aerodynamics. Second, removal of the motor is typically required to service the steering via repair or replacement of many of these parts.
A second disadvantage of this steering system is the inability to selectively change the steering ratio (defined as the functional relationship between the steering angle of the handlebars or steering wheel and the turning radius of the vehicle) to achieve the "optimum feel" desired by a particular driver for a particular circumstance. For example, on a vehicle used for racing on a short course with sharp turns, less movement of the handlebars would be desirable to achieve the desired turning radius compared to a vehicle used to travel longer distances over extended periods of time, which would perform better using a lower ratio providing more leverage in the handlebars for the operator.
A third disadvantage to the conventional steering system occurs when the steerable ski or wheel encounters a rock or tree or other impediment. Such an impact generally results in one or more parts fracturing or bending rendering the vehicle unusable. Due to the location of many of these parts beneath the motor, repair/replacement is not easily effected in the field and the vehicle must frequently be transported to a garage for repair requiring that the engine be pulled to provide access to the damaged part. Deep snow, mud and rugged terrain, combined with the size and weight of the vehicle can make this a very difficult and unpleasant task.
Yet a fourth disadvantage of this steering system lies in its rigidity. The vibrations experienced by the skis or wheels are transmitted through the system to the handlebars/steering wheel into the steerer's hands and arms producing fatigue. Long term, continuous exposure to such vibrations can result in nerve damage and a condition known as "white hand".
These disadvantages of the conventional steering system for off-road vehicles are exacerbated by the increasing capabilities of the drive systems (size and power of the engine) and the rigorous use to which the vehicles are put (i.e., racing). In an attempt to satisfy the demands of the consumer, manufacturers are producing faster, more powerful machines than ever before. These more powerful vehicles when used in the more rigorous conditions associated with racing, are over-driving the capabilities of the steering systems and accelerating failures due to wear and breakage.
All of these disadvantages are addressed by the steering mechanism of the present invention. A steering post is rotatably attached to a chassis. The steering post may be operated by a set of handle bars or a steering wheel affixed to its upper end. To the lower end of the steering post is attached a drive pulley which engages a segment of a drive belt. The two ends of the drive belt are attached to ends of a drag link by two retainers. Tension in the belt is maintained by a pair of idler rollers which may be manually or automatically (spring-biased) adjusted to provide proper tension in the belt.
The drag link is itself pivotally attached to the chassis by a pair of idler arms to permit the drag link to slide laterally to the left and right to steer the vehicle. Each end of the drag link is, in turn, attached to a spindle by means of heim joint, a tie rod tube and a tie rod. Each spindle is connected to either a steerable ski or wheel, depending on the nature of the off-road vehicle.
The present steering system is simple, light weight, reliable and precise. In addition, the steering ratio can be easily changed by replacing the drive pulley with another having a larger or smaller diameter. While the improved system is less prone to wear and breakage due in part to the fewer number of parts, servicing is greatly simplified since the entire mechanism is positioned above/in front of the drive train. This also provides a lower center of gravity for the vehicle, a lower profile and a more aerodynamic design. The steering mechanism is easier for the driver to operate, results in the transmission of less vibration into the driver's hands, reduces the free play of the steering mechanism and provides a more precise feel for the driver.
Various other features, advantages and characteristics of the present invention will become apparent to one of ordinary skill in the art after a reading of the following specification.